In recent years, performances of parts used in a computer and the other information processing apparatuses have been improved significantly. For example, performance improvement of a semiconductor memory, such as a static random access memory (SRAM), a dynamic random access memory (DRAM), and so on, a central processing unit (CPU): processor, a switching large scale integration (LSI), and so on, is remarkable.
And with the performance improvement of these semiconductor memories, processors, and so on, situations are arising where it becomes difficult to improve system performance unless signal transmission rates among individual parts and components are improved.
That is to say, it becomes important to improve signal transmission rates between a main memory, such as a DRAM and so on, and a processor, between servers through a network, between boards (printed wiring boards), or between semiconductor chips, and between elements and circuit blocks in one chip.
Incidentally, in order to increase a signal transfer rate, for example it is preferable to employ a serial transmission method that is capable of excluding skew between bits, which is caused by differences of wiring lines, and becomes a problem in a parallel transmission method.
Specifically, a communication speed of a circuit that transmits and receives data at a high speed (for example, a serializer and deserializer (SerDes): parallel-serial conversion circuit almost reaches to tens of Gbps. And in Ethernet (a registered trademark), a transmission standard of 25 Gbps has already appeared. Further, standardization of 40 Gbps and 56 Gbps (for example, CEI-56G-VSR) is in progress.
Incidentally, to date, proposals have been made of various timing control circuits that make it possible to correct data transmission and reception at a high data transfer rate.
Related-art techniques have been disclosed in Japanese Laid-open Patent Publication Nos. 2007-082147, 2001-044976, 5-022274, and 2009-212735, for examples.
To date, SerDes has been using a phase interpolator in order to adjust timings of input data and a clock, for example. The use of the phase interpolator makes it possible to correctly adjust data sampling point. However, there are problems in that an occupied area of a circuit becomes large, and the power consumption increases.